footer {
  position: fixed;
  left: 0;
  bottom: 0;
  line-height: 50px;
  height: 50px;
  width: 100%;
  text-align: center;
  background-color: white;
}
footer ul {
  list-style: none;
  display: flex;
}

footer ul li {
  /* 平分 */
  flex: 1;
}

.active {
  color: red;
}
